Add 'ClassModelLoader' - Instantiates a specific class for the model.

src/main/java/codechicken/lib/datagen/ItemModelProvider.java

@@ -2,6 +2,7 @@
 
 import com.google.gson.JsonArray;
 import com.google.gson.JsonObject;
+import net.minecraft.client.resources.model.BakedModel;
 import net.minecraft.data.PackOutput;
 import net.minecraft.resources.ResourceLocation;
 import net.minecraft.world.item.Item;
@@ -17,6 +18,8 @@
 import org.apache.logging.log4j.Logger;
 import org.jetbrains.annotations.Nullable;
 
+import java.lang.reflect.Constructor;
+import java.lang.reflect.Modifier;
 import java.util.*;
 import java.util.function.Consumer;
 import java.util.function.Function;
@@ -138,6 +141,18 @@ protected void simpleItemBlock(Block block) {
                 .parent(new ModelFile.UncheckedModelFile(modLoc("block/" + name(block))))
                 .noTexture();
     }
+
+    protected SimpleItemModelBuilder clazz(Supplier<? extends Item> item, Class<? extends BakedModel> clazz) {
+        return clazz(item.get(), clazz);
+    }
+
+    protected SimpleItemModelBuilder clazz(ItemLike item, Class<? extends BakedModel> clazz) {
+        return generated(item)
+                .noTexture()
+                .customLoader(ClassCustomLoaderBuilder::new)
+                .clazz(clazz)
+                .end();
+    }
     //endregion
 
     private SimpleItemModelBuilder makeNested(ItemLike item) {
@@ -328,6 +343,35 @@ protected JsonObject toJson(JsonObject json) {
         }
     }
 
+    public static class ClassCustomLoaderBuilder extends CustomLoaderBuilder {
+
+        private @Nullable Class<? extends BakedModel> clazz;
+
+        protected ClassCustomLoaderBuilder(SimpleItemModelBuilder parent) {
+            super(new ResourceLocation(MOD_ID, "class"), parent);
+        }
+
+        public ClassCustomLoaderBuilder clazz(Class<? extends BakedModel> clazz) {
+            try {
+                Constructor<?> ctor = clazz.getConstructor();
+                if (!Modifier.isPublic(ctor.getModifiers())) {
+                    throw new IllegalArgumentException("Expected single no-args public constructor.");
+                }
+            } catch (NoSuchMethodException ex) {
+                throw new IllegalStateException("Expected single no-args public constructor.", ex);
+            }
+            this.clazz = clazz;
+            return this;
+        }
+
+        @Override
+        protected JsonObject toJson(JsonObject json) {
+            super.toJson(json);
+            json.addProperty("class", Objects.requireNonNull(clazz).getName());
+            return json;
+        }
+    }
+
     public static class CompositeLoaderBuilder extends CustomLoaderBuilder {
 
         private final Map<String, SimpleItemModelBuilder> children = new LinkedHashMap<>();

src/main/java/codechicken/lib/internal/ClientInit.java

@@ -4,6 +4,7 @@
 import codechicken.lib.config.ConfigCategory;
 import codechicken.lib.config.ConfigSyncManager;
 import codechicken.lib.model.CompositeItemModel;
+import codechicken.lib.model.ClassModelLoader;
 import codechicken.lib.render.CCRenderEventHandler;
 import codechicken.lib.render.block.BlockRenderingRegistry;
 import net.covers1624.quack.util.CrashLock;
@@ -71,5 +72,6 @@ private static void onClientDisconnected(ClientPlayerNetworkEvent.LoggingOut eve
 
     private static void onRegisterGeometryLoaders(ModelEvent.RegisterGeometryLoaders event) {
         event.register("item_composite", new CompositeItemModel());
+        event.register("class", new ClassModelLoader());
     }
 }

src/main/java/codechicken/lib/model/ClassModelLoader.java

@@ -0,0 +1,51 @@
+package codechicken.lib.model;
+
+import com.google.gson.JsonDeserializationContext;
+import com.google.gson.JsonObject;
+import com.google.gson.JsonParseException;
+import net.covers1624.quack.gson.JsonUtils;
+import net.minecraft.client.renderer.block.model.ItemOverrides;
+import net.minecraft.client.renderer.texture.TextureAtlasSprite;
+import net.minecraft.client.resources.model.BakedModel;
+import net.minecraft.client.resources.model.Material;
+import net.minecraft.client.resources.model.ModelBaker;
+import net.minecraft.client.resources.model.ModelState;
+import net.minecraft.resources.ResourceLocation;
+import net.minecraftforge.client.model.geometry.IGeometryBakingContext;
+import net.minecraftforge.client.model.geometry.IGeometryLoader;
+import net.minecraftforge.client.model.geometry.IUnbakedGeometry;
+
+import java.lang.reflect.Constructor;
+import java.lang.reflect.InvocationTargetException;
+import java.util.function.Function;
+
+import static net.covers1624.quack.util.SneakyUtils.unsafeCast;
+
+/**
+ * Created by covers1624 on 13/11/23.
+ */
+public class ClassModelLoader implements IGeometryLoader<ClassModelLoader.Geometry> {
+
+    @Override
+    public Geometry read(JsonObject jsonObject, JsonDeserializationContext deserializationContext) throws JsonParseException {
+        try {
+            Class<?> clazz = Class.forName(JsonUtils.getString(jsonObject, "class"));
+            Constructor<? extends BakedModel> ctor = unsafeCast(clazz.getConstructor());
+            return new Geometry(ctor);
+        } catch (ClassNotFoundException | NoSuchMethodException ex) {
+            throw new RuntimeException(ex);
+        }
+    }
+
+    public record Geometry(Constructor<? extends BakedModel> ctor) implements IUnbakedGeometry<Geometry> {
+
+        @Override
+        public BakedModel bake(IGeometryBakingContext context, ModelBaker baker, Function<Material, TextureAtlasSprite> spriteGetter, ModelState modelState, ItemOverrides overrides, ResourceLocation modelLocation) {
+            try {
+                return ctor.newInstance();
+            } catch (InstantiationException | IllegalAccessException | InvocationTargetException ex) {
+                throw new RuntimeException("Failed to construct class.", ex);
+            }
+        }
+    }
+}